pic16bit: Use global MICROPY_NO_ALLOCA setting.

pic16bit/mpconfigport.h

@@ -63,6 +63,7 @@
 #define MICROPY_CPYTHON_COMPAT      (0)
 #define MICROPY_LONGINT_IMPL        (MICROPY_LONGINT_IMPL_MPZ)
 #define MICROPY_FLOAT_IMPL          (MICROPY_FLOAT_IMPL_NONE)
+#define MICROPY_NO_ALLOCA           (1)
 
 // type definitions for the specific machine
 
@@ -98,9 +99,6 @@ extern const struct _mp_obj_module_t pyb_module;
 #define MICROPY_PORT_BUILTIN_MODULES \
     { MP_OBJ_NEW_QSTR(MP_QSTR_pyb), (mp_obj_t)&pyb_module }, \
 
-// We need to provide a declaration/definition of alloca()
-#define alloca(x) (void*)m_new(byte, (x))
-
 #define MP_STATE_PORT MP_STATE_VM
 
 #define MICROPY_PORT_ROOT_POINTERS \